Reconstructing Global Precipitation for the 20 th Century

1. Reconstructing Global Precipitation for the 20th Century Presented by Thomas M. Smith

2. Requirement, Science, and Benefit Requirement/Objective • Climate: • Little or no oceanic precipitation sampling in pre-satellite era (before 1979) • Need analyses to estimate oceanic climate scale variations • Evaluate land & ocean multi-decadal precipitation changes beginning 1900 Science • How much has oceanic precipitation changed over the 20th century? • How well can climate-model precipitation be validated? Benefit • Addresses NOAA’s research plans to understand and predict changes in the global hydrologic cycle, included in water and weather and climate research • Analysis of ocean precipitation can be used to validate and improve climate models, needed for IPCC and other international & national assessments • Improved assessments and improved climate models are needed for studies of changing fresh-water availability, needed for planning for future societal needs

3. Challenges and Path Forward • Science challenges • Improving precipitation analyses from satellites and reconstructions • Satellite-based analysis improvements to continue at STAR/CICS, with partners including U. MD/ESSIC, NCDC, and NASA/GSFC • Improving climate model representation of precipitation variations • Will work with other national and international groups to help validate climate models • Next steps • Documentation and making reconstruction available • Investigating ways to improve the reconstruction • Transition Path • Making reconstruction available to users • Plans to update the reconstruction for climate possible studies and monitoring

4. Basics of the Reconstruction Problem • In Situ Sampling • Land sampling for 20th century from analyses: Climate Research Unit of Univ. of East Anglia (CRU), Global Precipitation Climatology Center (GPCC), Global Historical Climate Network (GHCN) • Time series of % of average annual global area sampled by each analysis • Sparse oceanic sampling over most of 20th century: need to use satellite & in situ data together to understand ocean-area changes since 1900

5. Reconstruction Methods • Two Reconstructions • Both require high-quality satellite analyses to generate statistics needed for historical analyses • STAR contributes to the development and improvement of satellite-based analyses needed • 1. Monthly, fitting gauge data to spatial covariance functions, resolves land and oceanic interannual variations • 2. Annual, Canonical Correlation Analysis (CCA) precipitation from sea-surface temperature & sea-level pressure, resolves oceanic multi-decadal variations • Comparison analyses: Global Precipitation Climatology Project (GPCP), Global Historical Climate Network (CHCN), IPCC Assessment report 4 ensemble of coupled models (AR4) Smith, T. M., M. R. P. Sapiano, and P. A. Arkin, 2008: Historical Reconstruction of Monthly Oceanic Precipitation (1900-2006), J. Geophys. Res., 113, D17115, doi:10.1029/2008JD009851. Smith, T. M., P. A. Arkin, and M. R. P. Sapiano, 2009: Reconstruction of near-global annual precipitation using correlations with sea surface temperature and sea level pressure. J. Geophys. Res., 114, D12107, doi:10.1029/2008JD011580. Near global averages of CCA annual land gauge-sampled (upper) and ocean low-frequency (lower).

6. Merged Reconstruction • Merged analyses • Fitting gauge data to spatial modes and the CCA (from the previous slide) are merged • A global monthly analysis is the results • Comparisons to AR4 model ensemble • Joint Empirical Analysis Function analysis of low-pass normalized data from each • Shows were the model ensemble climate change signal is consistent with the analysis, and where it has systematic biases Smith, T. M., M. R. P. Sapiano, and P. A. Arkin, 2009: Modes of multi-decadal oceanic precipitation variations from a reconstruction and AR4 model output for the 20th century, Geophys. Res. Lett., 36, L14708, doi:10.1029/2009GL039234. T.M. Smith, P.A. Arkin, M.R.P. Sapiano, C.-Y. Chang, 2010: Merged statistical analyses of historical monthly precipitation anomalies beginning 1900. Submitted to J. Climate. P.A. Arkin, T. M. Smith, M.R.P. Sapiano, J. Janowiak, 2010: Challenges in Observing Changes in Global Precipitation. To be submitted to Environmental Research Letters.

7. Challenges and Path Forward • Science challenges • Improving precipitation analyses from satellites and reconstructions • Satellite-based analysis improvements to continue at STAR/CICS, with partners including U. MD/ESSIC, NCDC, and NASA/GSFC • Improving climate model representation of precipitation variations • Will work with other national and international groups to help validate climate models • Next steps • Documentation and making reconstruction available • Investigating ways to improve the reconstruction • Transition Path • Making reconstruction available to users • Plans to update the reconstruction for climate possible studies and monitoring